Ace genotype which correlates with improved success in sodium excretion in hypertensives with exercise

ABSTRACT

A method of increasing sodium excretion levels in a hypertensive subject by identifying a subject having an II genotype for an angiotensin converting enzyme gene, and engaging the subject in limited exercise training for a period of time sufficient to increase the subject&#39;s sodium excretion levels.

This nonprovisional application claims the benefit of U.S. ProvisionalApplication No. 60/247,951, filed Nov. 13, 2000.

FIELD OF THE INVENTION

The present invention relates to identifying an ACE genotype whichcorrelate with improved success in sodium excretion in hypertensiveindividuals engaged in exercise training.

BACKGROUND OF THE INVENTION

Regular endurance exercise has been shown to lower blood pressure inhypertensive patients (see, e.g., Hagberg et al., J. Cardiov. Risk, vol.2, pp. 296 et seq., 1995) and is widely recommended as an initialnon-pharmacological treatment. One of the potential mechanismsunderlying this effect of exercise training is an increase in sodiumexcretion. Unfortunately, some individuals, no matter how rigorouslythey exercise, are unable to improve their conditions, while othersbenefit to a much greater extent than predicted. These resultsunderscore the fact that many factors contribute to an individual'swell-being. Such factors include, for example, behaviors such as dietand exercise, genetic makeup, and environment. While behavior andenvironment can be controlled, altered or regulated, an individual'sgenetic makeup is essentially predetermined and set at birth.

Angiotensin converting enzyme (ACE) is the enzyme responsible forcatalyzing the conversion of angiotensin I, a relatively inactive tissueand plasma vasopressor hormone, into the potent and highly activevasopressor hormone angiotensin II. This cascade of reactions is part ofthe renin-angiotensin-aldosterone system that has long been known to bean important regulator of arteriolar relaxation and vasoconstriction,and hence blood pressure, in humans and animals. The ACE gene ispolymorphic with two common alleles designated “I” and “D”, resulting inthree genotypes: “II”, “ID” and “DD”. The “D” allele has a 287-base pairmarker in intron 16 of the ACE gene deleted, whereas the “I” allele hasthe 287-base pair marker inserted. The “D” allele is associated withincreased levels of ACE in both plasma and ventricular tissues.Increased levels of ACE contributes to increased myocardial and vascularsmooth muscle growth and increased arteriolar vasoconstriction. Thus,the presence of the “D” allele is hypothesized to have deleteriouseffects on the cardiovascular system, and, in fact, the “D” allele hasbeen associated with increased risk of left ventricular hypertrophy,cardiovascular disease, and sudden cardiovascular death. Prior studieshave sought to determine if an association exists between ACE “DD”genotype and blood pressure regulation. Results from human studies havebeen mixed, with most studies unable to identify an association betweenACE gene variants and blood pressure in Caucasian and African Americans.(Schunkert et al., Hypertension, vol. 29, pp. 628 et seq., 1997; Rotimiet al., Hypertension, vol. 24, pp. 591 et seq., 1994.) However, onestudy found an association between hypertension and the “D” allele inAfrican Americans. (Duru et al. Am. J. Hypertension, vol. 7, pp. 759 etseq., 1994.)

Published PCT application WO 99/45383 (Hagberg et al.) discloses thathypertensive individuals with different ACE genotypes exhibiteddifferent degrees of success in reducing their blood pressure levelsthrough exercise. The results were dependent on the duration of theexercise protocol. The inventors found that those individuals having an“II” or “ID” genotype exhibited more reduction in blood pressure levelsthan those with a “DD” genotype, after the long-term exercise protocol.However, after the most short-term exercise protocol, those subjectshaving “II” or “DD” genotypes exhibited more reduction in blood pressurelevels than those with “ID” genotypes. After a limited exercise protocolthat was more extensive than the short-term exercise protocol, thosesubjects having an “II” genotype exhibit more reduction in bloodpressure levels than those with “ID” or “DD” genotypes.

In a separate study, it was reported that sodium excretion rate inAfrican American hypertensive women increased 37% after 7 days ofexercise. (Brown et al., Hypertension, vol. 30, pp. 1549 et seq., 1997.)However, no genotyping was reported in this study, and thus there was noidentification with respect to whether those individuals with a certaingenotype derived more benefit from the exercise. An object of thepresent invention is to identify those hypertensive individuals who aremore likely to benefit from exercise in increasing sodium excretion,based on their genotype.

SUMMARY OF THE INVENTION

The present inventors have discovered that the angiotensin convertingenzyme (ACE) gene serves as a genetic marker which positively correlateswith improved success in increasing sodium excretion levels inhypertensive individuals. Specifically, the inventors have found thatthose individuals possessing the “II” ACE genotype increased theirsodium excretion levels significantly more than those individualspossessing either the “ID” or “DD” ACE genotype. The present inventionis directed to a method of increasing sodium excretion levels in ahypertensive subject, comprising:

identifying a hypertensive subject having an II genotype for anangiotensin converting enzyme gene; and

engaging the subject in limited exercise training for a period of timesufficient to increase the subject's sodium excretion levels.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the sodium excretion levels of thirteen subjects, groupedby ACE genotype, before and after limited exercise training.

FIG. 2 shows the change in sodium excretion levels of the same thirteensubjects, grouped by either having or not having a “D” allele.

DETAILED DESCRIPTION OF THE INVENTION

The inventors have found that the ACE genetic marker positivelycorrelates with improved success in increasing sodium excretion levelsin hypertensive individuals, such that those individuals having an IIgenotype have improved success as compared with other genetic makeup atthe same gene locus.

Sodium excretion may be measured in body fluids such as urine, sweat,saliva or blood. After establishing baseline levels, in order todetermine the change in sodium excretion levels, sample collection canoccur at any time period before or after a single course of exercise.However, it is preferred that sample collection be conducted 0-24 hoursafter a single course of exercise, most preferably about 14-18 hoursafter a single course of exercise.

The term “single course of exercise”, as used throughout thisapplication, means a cardiovascular exercise session of any type whichis conducted during one day. An exercise session may comprise anaerobics class, treadmill training, step machine, cycling, or any othersuitable cardiovascular exercise regimen. For most cases, exercise maybe completed in, for example, 30 minutes to 3 hours, preferably between45 minutes and 90 minutes, with optional brief rest periods of 3-15minutes, however this amount would vary depending on the health andendurance of the subject. It is preferred that the exercise regimen beselected to ensure that each subject's exercise heart rate correspondsto between 50 and 80%, most preferably about 65%, of their heart ratereserve.

The term “limited exercise” means about 5-9 single courses of exercise,preferably about 6-8, or 7 single courses of exercise, over the exerciseperiod. The exercise period in the case of a limited exercise protocolis preferably about 5-30 days, more preferred about 5-20 days, mostpreferred about 5-12 days. The exercise period can also be a dailysingle course of exercise (i.e., daily exercise for about 5-9 days,depending on the number of single courses of exercise in the protocol).

The time between exercise periods may be from 2-60 days or more. Theterm “between exercise periods” means that time during which the subjectis not in a limited exercise program.

The present inventors have discovered that hypertensive individuals withdifferent ACE genotypes exhibit different degrees of success inincreasing their sodium excretion levels through exercise. These resultscould not have been predicted from initial patient screening.

The inventors have found that those individuals having “II” genotypeexhibit more increase in sodium excretion levels than those with “ID” or“DD” genotypes, after limited exercise.

EXAMPLES Example 1 Variations in Increase of Sodium Excretion inThirteen (13) Subjects After Limited Exercise

Thirteen subjects aged 5±8 years were obese (body fat>35%), sedentary(VO₂max 21.8±4.8 ml/kg/min), hypertensive (BP 143±3 over 91±2 mmHg) maleand female African Americans. The insertion/deletion ACE gene (“II” n=5;“ID” n=4; “DD” n=4) polymorphism was determined using standard PCRprocedures.

Exercise consisted of seven (7) consecutive days of treadmill walkingand stationary cycling for 50 min/d at 65% of heart rate reserve. Sodiumexcretion was determined by 24-hour urine collection at baseline, andbeginning 14-18 hours after the last exercise session. Subjects consumeddiets identical in macronutrient and sodium content during the testingperiods. Baseline sodium excretion, fasting insulin and glucose levels,percent body fat, VO₂max and casual mean blood pressure (MBP) weresimilar in the ACE genotype groups, as shown in Table 1 below: TABLE 1ACE Genotype Variable II (n = 5) ID (n = 4) DD (n = 4) Age (yrs) 51 ± 656 ± 9  45 ± 5 Body Fat (%)  42.4 ± 13.4 39.2 ± 2.9  44.8 ± 2.0 VO₂max(ml/kg/min) 22.5 ± 6.6 24.2 ± 3.7  19.9 ± 2.0 MBP (mmHg) 110.3 ± 2.4 108.1 ± 1.8  113.2 ± 3.5  Fasting Insulin (uU/ml)  8.4 ± 2.3 9.8 ± 5.111.8 ± 5.0 Urinary Sodium (mmol/d) 119 ± 26 102 ± 16  138. ± 11 Values are expressed as mean ± SD

After seven days of exercise training, sodium excretion wassignificantly increased in all three genotype groups, as shown in Table2 below: TABLE 2 ACE Genotype Variable II (n = 5) ID (n = 4) DD (n = 4)Urinary Sodium 186 ± 42 125 ± 13 160 ± 12 (p = 0.024) (mmol/d) (p =0.03) (p = 0.043)Values are expressed as mean ± SD

The increase in sodium excretion in response to limited exercisetraining tended to be higher in the “II” genotype group (57% increase)compared to the “ID” (23% increase) and “DD” (16% increase) genotypegroups (p=0.079). FIG. 1 shows the “before and after” results in graphform. FIG. 2 shows the change in sodium excretion levels in the subjectsgrouped by either having or not having a “D” allele.

Example 2 Variations in Increase of Sodium Excretion in Thirty (30)Subjects After Limited Exercise

The study of Example 1 was increased to a total of thirty male andfemale African American subjects, aged 51±8 years, obese (body fat>35%),sedentary (VO₂max 21.8±4.8 ml/kg/min) and hypertensive (BP 145±4 over90±3 mmHg). The insertion/deletion ACE gene (“II” n=8; “ID” n=10; “DD”n=12) polymorphism was determined using standard PCR procedures.

Exercise consisted of 7 consecutive days of treadmill walking andstationary cycling for 50 min/d at 65% of heart rate reserve. Sodiumexcretion was determined by 24-hour urine collection at baseline andbeginning 14-18 hours after the last exercise session. Subjects consumeddiets identical in macronutrient and sodium content during the testingperiods. Baseline sodium excretion, fasting insulin and glucose levels,percent body fat, VO₂max, and casual mean blood pressure (MBP) weresimilar in the ACE genotype groups.

After seven days of exercise training, sodium excretion wassignificantly increased in all three genotype groups, as shown in Table3: TABLE 3 ACE Genotype II (n = 5) ID (n = 4) DD (n = 4) Urinary Sodium(before) (mmol/d) 119 ± 26 110 ± 16 138 ± 11 Urinary Sodium (after)(mmol/d) 166 ± 42 130 ± 13 160 ± 12 P value 0.04 0.04 0.02Values are expressed as mean ± SD

The increase in sodium excretion tended to be higher in the “II”genotype group (39% increase) compared to the “ID” (18% increase) and“DD” (16% increase) genotype groups (p=0.06).

1. A method of increasing sodium excretion levels in a hypertensivesubject, the method comprising: identifying a hypertensive subjecthaving an II genotype for an angiotensin converting enzyme gene, whereinthe subject is in need of increased sodium excretion levels; andengaging the subject in limited exercise training for a period of timesufficient to increase sodium excretion levels in the subject.